Now, nearly half of the thermal power plants in the country, including over 20,000 MW capacity stations of state-run NTPC, are reeling under coal shortage with stocks to last less than a week, according to official data.

According to latest CEA (Central Electricity Authority) data (July 15), 46 coal-based generating stations, of the total list of 100, reported fuel stock for less than seven days.

NTPC, the country's largest power producer and also the biggest consumer of domestic coal, is the worst sufferer as eight of its 23 electricity generating stations have stock to last mere two days, the data said.

State-run NTPC has asked the power ministry to ensure more coal is sent to six of its plants because they do not have enough stocks to weather even a "small" disruption in supplies. The fuel reserves are sufficient for only up to two days, it has warned.

These six plants have a combined capacity of 16,840 megawatts or 15% of India's total energy capacity from coal-fired plants.

India, which uses coal to generate more than half of its electricity, is struggling to provide enough power to meet rising demand and the country is regularly hit with blackouts.

"With the ensuing monsoon, it will become more difficult to replenish the coal stocks and in case of even a small disruption, the total power generation at these stations will be adversely affected," NTPC Chairman Arup Roy Choudhury said in a July 14 letter to the power ministry.

Choudhury was not immediately available to provide an update on stock levels on Thursday.

State behemoth Coal India, the world's largest coal miner, has failed to raise its output fast enough, forcing India to import millions of tonnes of the black rock for its thermal power plants.

Insufficient reserves are particularly problematic this year. Weak monsoon rains have limited the output from hydropower plants, which provide about a fifth of India's energy, putting added pressure on the thermal plants to raise output.

Last week power minister Piyush Goyal urged power companies to raise thermal coal imports after saying that 26 out of 100 coal-based power plants in India had "super critical" stocks — or only enough to meet requirements for less than four days.

The Centre is now looking at help from states to tide over a potentially crippling power situation.